The detection and tracking of objects such as airplanes, missiles, or other very large projectiles can be achieved using radar. Radar detection and tracking can be used to locate the aircraft, detect incoming missiles, and aim radar controlled guns. However, the use of radar is not without disadvantages. In radar detection and tracking, the radar must radiate energy. The energy emitted by the radar enables enemies or other interested parties to determine that radar is being used and further to determine the location of the source of the radar.
Detection and tracking of certain objects has also been achieved using infrared radiation (IR) detection. IR detection has the advantage that is passive. That is, IR detection devices do not emit radiation, but instead, detect heat or infrared radiation emitted from an object. Thus, because an IR detector does not emit radiation, an object being detected and tracked using an IR detector can not easily determine the source or location of the IR detector.
IR detection of projectiles such as missiles has been accomplished by observing hot-gas plumes emitted from the rear of projectiles, and the rear surfaces of the projectiles which are heated by the hot-gases. Unfortunately, the detection and tracking of the rear surfaces of projectiles has the disadvantage that its geometry is only well suited to detecting and tracking one's own projectile as it moves away from its origin wherein the IR detector is located. Although IR detection of a missile moving towards an observer has been accomplished, IR detection of a projectile is not particularly well suited to detecting and tracking a projectile as it moves towards the IR detector.
Some modern IR detectors have recently been developed with sufficient sensitivity to detect items such as leading edges of airplane wings. IR detection of such items is accomplished by observing the leading edge of the projectile as it is warmed due to friction occurring while the projectile passes through the atmosphere. However, such detectors are at present only useful for detecting and tracking the leading edges of large projectiles or very large surface areas such as are found on airplane wings. That is, the IR emitted from smaller surfaces or projectiles is difficult to observe due to reduced intensity and also because the ratio of the projectile's infrared radiation vs. the infrared radiation emitted by the background is extremely low. Therefore, using present methods of IR detection, the IR emitted from smaller projectiles can not be discerned from constant background IR emissions.
Thus, a need exists for a detection and tracking method and device, which does not emit radiation, can be used to detect and track items without regard to the direction in which the projectile is moving, and which is not limited to detecting and tracking only the leading edges of large projectiles or very large surface areas.